Recent studies focus on the application of fuel-cell power generating systems to electric and hybrid vehicles driven by secondary batteries. In specific, in response to significant decreases in the charging rates (states of charge; SOC) of the secondary batteries, the fuel cells generate power for charging the secondary batteries and driving the vehicles to compensate for the power shortage. Such fuel cells functioning as auxiliary power sources can increase the running distances of the vehicles at high fuel efficiency without increased capacities of the secondary batteries (e.g., refer to PTLs 1 and 2).
A typical fuel cell experiences temporary increases in the electrode potential caused by fluctuations in load and the switching between the start and stop of the fuel cell, resulting in deterioration of carriers and catalyst. Such deterioration impairs the performance of the fuel cell and the running performance of the vehicle. Eagerly anticipated is a more durable and reliable fuel cell.
A measure under consideration to solve this problem without deterioration is an improved operation of a fuel cell. For example, PTL 1 discloses control for driving a fuel cell to charge a secondary battery when the charging rate of the secondary battery reaches the lower limit, and controlling the fuel cell to be an idling mode when the charging rate of the secondary battery reaches the upper limit. The prevention of frequent restarts (stops and starts) of the fuel cell can maintain high system efficiency.